1. Monohybrid & Dihybrid Crosses
Review
Monohybrid & Dihybrid Crosses

2. DOMINANT/RECESSIVE T t capital Dominant Recessive lower-case
_____________ allele is represented by a ____________ letter. (usually the first letter of the trait)
____________ allele is represented by the SAME
_________________ letter.
EX: Tall = ______
Short =______
capital
Recessive
lower-case T t
NOT S for short

3. HOMOZYGOUS HETEROZYGOUS
When both alleles in the pair are the _______, the organism is _______________ or __________
EX: ____ or ___
When both alleles in the pair are _____________, the organism is
_________________ or _____________
Ex: ____
SAME
HOMOZYGOUS PURE
TT tt
DIFFERENT
HETEROZYGOUS HYBRID Tt

4. PHENOTYPE/GENOTYPE
The ________________ of an organism is its _____________
The ____________of an organism is
its _____________
genetic makeup
GENOTYPE
appearance
PHENOTYPE

5. MAKING A CROSS for only a __________ trait = ____________________
ONE GENE
MONOHYBRID CROSS
A Punnett square for a MONOHYBRID CROSS looks like this:

6. PUNNETT SQUARES
are used to show possible offspring from a cross between 2 parents
_______________ go at
top and on left side
Boxes show ____________ ___________________
Parent alleles
T T T t
possible offspring combinations

7. STEPS FOR MAKING CROSSES
Figure out parent alleles
Choose Punnett size
Put in parent gametes
Fill in offspring combinations
probabilities phenotypes genotypes
1. ___________ what _________________ are
2. ________correct__________ square __________
3. ______ possible_______________________
4. ______ boxes with _____________________
5. Determine ____________of_____________& ____________

8. T t TALL = ____ SHORT = ____ IN PEA PLANTS Tall is dominant over short
LET’S MAKE A CROSS!
PURE TALL PURE SHORT X

9. PURE TALL parent What are the parent alleles?
T T _________
HOMOZYGOUS  
What gametes
can it make? T T

10. PURE SHORT parent What are the parent alleles?
t t _________
HOMOZYGOUS  
What gametes
can it make? t t

11. T t T t T t T t T t _____ of the offspring ____ % ___/4 will be ALL
100 4
T t
T t Tt
TALL
GENOTYPE _____ PHENOTYPE _______

12. HYBRID TALL parent What are the parent alleles?
T t _________
HETEROZYGOUS  
What gametes
can it make? T t

13. T t T t T t T T T t t t GENOTYPES ¼ = _____ ½ = _____ TT Tt tt 3/4 75
TALL
PHENOTYPES ____ or ____% _________
____ or ____% _________
1/4 25
SHORT

14. PRACTICE MAKING GAMETES for a MONOHYBRID CROSS
Tall = ____ Round seeds = ___
Short = ____ Wrinkled seeds = ___ T t r

15. What are the possible gametes?
Homozygous Tall parent =
What gametes can it produce?
T T   T T

16. What are the possible gametes?
PURE wrinkled parent =
What gametes can it produce? rr   r r

17. What are the possible gametes?
Heterozygous Round parent =
What gametes can it produce?
R r   R r

18. What are the possible gametes?
Hybrid Tall parent =
What gametes can it produce? Tt   T t

19. DIHYBRID CROSSES (2 traits)

20. Mendel also asked the question?
Does the gene that determines if a seed
is round or wrinkled have anything to
do with the gene for seed shape?
Must a seed that is yellow
also be round?

21. MAKING A CROSS with ___________________= ____________________
TWO gene traits
DIHYBRID CROSS
A Punnett square for a DIHYBRID CROSS looks like this:

22. Figure 11-10 Independent Assortment in Peas
Section 11-3

23. LET’S MAKE A DIHYBRID CROSS
HOMOZYGOUS
YELLOW ROUND
HOMOZYGOUS
GREEN WRINKLED
rryy
RRYY
1. ___________ what _________________ are
2. ________correct__________ square __________
3. ______ possible_______________________
4. ______ boxes with _____________________
5. Determine ____________of_____________& ____________
Figure out parent alleles
Choose Punnett size
Put in parent gametes
Fill in offspring combinations
probabilities phenotypes genotypes

24. LAW OF __________________________
the factors are distributed to gametes independently of other factors
INDEPENDENT ASSORTMENT
Image modified from:

25. PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES
THIS PARENT CAN MAKE?
HOMOZYGOUS ROUND YELLOW
Each gamete should get one of each kind of gene
R R Y Y
R Y
R Y
R Y
R Y
___________ ____________ _____________ _____________

26. PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES
THIS PARENT CAN MAKE?
Each gamete should get one of each kind of gene
HOMOZYGOUS WRINKLED GREEN
r r y y
r y
r y
r y
r y
___________ ____________ _____________ _____________

27. PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES
THIS PARENT CAN MAKE?
HETEROZYGOUS ROUND YELLOW
Each gamete should get one of each kind of gene
R r Y y
R Y
r y
r Y
R y
___________ ____________ _____________ _____________

28. RY RrYy ROUND YELLOW ry 100% of offspring = _______ genotype
RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy
RrYy
100% of offspring = _______ genotype
_______________________ phenotype
ROUND YELLOW

29. X R r Y y R r Y y MAKE ANOTHER CROSS HETEROZYGOUS ROUND YELLOW

30. POSSIBLE PARENT GAMETES?RY ry Ry ry

31. heterozygous dihybrid 9:3:3:1RY Ry rY ry
____ Round & Yellow
____ Round & green
____ Wrinkled & yellow
____ wrinkled & green 9 RY Ry rY ry
RRYY RRYy RrYY RrYy
RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy
RrYy Rryy rrYy rryy 3 3 1
heterozygous dihybrid
Sign of a ______________________ cross is a
_____________ ratio in offspring.
9:3:3:1

32. __________ratio is a clue that it’s a 9
____ ____________ TRAIT 1 ; ____________ TRAIT 2
____ ____________ TRAIT 1; _____________ TRAIT 2
____ ____________ TRAIT 1; _____________ TRAIT 2
dominant dominant 3
dominant recessive 3
recessive dominant 1
recessive recessive
__________ratio is a clue that it’s a
____________________________cross
9:3:3:1
HETEROZYGOUS TWO gene

33. PRACTICE MAKING GAMETES for DIHYBRID CROSSES

34. What are the possible gametes?
R R T T
pure round & pure tall = __________
____ ____ _____ ______
What gametes can it produce?    
R T
R T
R T
R T

35. What are the possible gametes?
T t R R
Heterozygous Tall = __________
& pure round
____ ____ _____ ______
What gametes can it produce?    
T R
t R
t R
T R

36. What are the possible gametes?
T t r r
Hybrid tall = __________
& pure wrinkled
____ ____ _____ ______
What gametes can it produce?    
T r
t r
t r
T r

37. What are the possible gametes?
T t R r
Heterozygous tall = __________
& hybrid round
____ ____ _____ ______
What gametes can it produce?    
T R
t r
t R
T r

38. The Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.
The Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.
The Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

39. INDEPENDENT ASSORTMENT
MENDEL'S GENETIC LAWS
Summary:
LAW
PARENT CROSS
OFFSPRING
DOMINANCE
TT x tt tall x short
100% Tt tall
SEGREGATION
Tt x Tt tall x tall
75% tall 25% short
INDEPENDENT ASSORTMENT
RrGg x RrGg round & green x round & green
9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods